docs: def save_params(self, **kw):
          """
          Update the current calculation parameters and save engine_version
          """
          if ('hazard_calculation_id' in kw and
                  kw['hazard_calculation_id'] is None):
              del kw['hazard_calculation_id']
          vars(self.oqparam).update(**kw)
          self.datastore['oqparam'] = self.oqparam  # save the updated oqparam
          attrs = self.datastore['/'].attrs
          attrs['engine_version'] = engine_version
          attrs['date'] = datetime.now().isoformat()[:19]
          if 'checksum32' not in attrs:
              attrs['checksum32'] = readinput.get_checksum32(self.oqparam)
          self.datastore.flush()